Electrical switching for selection lines of a memory circuit



June 1954 R. w. REACH, JR, ETAL 3,137,797

ELECTRICAL SWITCHING FOR SELECTION LINES OF A MEMORY CIRCUIT Original Filed July 29. 1957 INVENTORS ROY m REA 0/, JR.

E. NORMA/V M. OUR/E- 0 [our MFR]: oya/v United States Patent C) 3,137,797 ELECTRICAL SWITCHING FOR SELECTION LINES OF A MEMORY CIRCUIT Roy W. Reach, Jr., Sudbury, Elmer T. Johnson, Wayland, and Norman M. Lourie, Newton Highlands, Mass, assignors, by mesne assignments, to Minneapolis- Honeywell Regulator Company, a corporation of Delaware Original application July 29, 1957, Ser. No. 674,905, now Patent No. 3,064,140, dated Nov. 13, 1962. Divided and this application May 15, 1962, Ser. No. 210,274

2 Claims. (Cl. 30788.5)

This application is a division of an application entitled Current Regulating Circuit for Switching Memory Elements and the Like, by Roy W. Reach, Jr., Elmer T. Johnson and Norman M. Lourie, Serial Number 674,905, filed July 29, 1957, now Patent No. 3,064,140, granted Nov. 13, 1962 which is assigned to the assignee of the present application.

A general object of the present invention is to provide a new and improved apparatus for generating electrical signal pulses. More specifically, the present invention is concerned with an apparatus for producing a signal pulse where the signal pulse is characterized by its having a constant current and by its being readily formed as a pulse of a reversible polarity.

The generation of pulses is frequently required for signaling circuits, switching circuits, and the like. The pulses required may be of plus or minus polarity depending upon the use to which the resultant signal is to be placed. Certain types of circuits require that the pulses used be of the constant current type, that is each pulse throughout its duration should have a constant current amplitude. A representative device requiring a constant current pulse is the coincident current memory which is widely used in digital data processing equipment. This coincident current memory utilizes bistable mag netic cores which are adapted to be switched between one or the other of its two stable states by current pulses applied to wires which thread the cores. The most effective switching current for these devices is a current having a constant amplitude. A more extensive discussion of coincident current memory devices will be found in an article by l. W. Forrester entitled, Digital Information Storage in Three Dimensions Using Magnetic Cores, in the Journal of Applied Physics, January, 1951, page 44.

It is desirable that the circuitry generating the constant current pulses be stable and that the pulses generated have an amplitude which is independent of the characteristics of any of the active elements in the circuit. Thus, if an electronic amplifier or switching device is used in the pulse generating circuit, the resultant output signal should have an amplitude which is independent of the internal characteristics of the electronic amplifier or switching device.

It is accordingly another more specific object of the present invention to provide a new and improved pulse generating circuit which produces an output pulse whose current amplitude is independent of the characteristics of the active elements of the circuit.

The foregoing object of the invention is achieved by a novel arrangement of a source of power which is connected to normally supply a constant current to a current sink. When an output pulse is desired, the current to the current sink is momentarily diverted to a load circuit and is then returned to the current sink. The diversion may be effected by an electronic switch which is adapted to be switched from a high impedance state where substantially no current will flow to a low im- 3,137,797. Patented June 16, 1964 pedance state where the current may flow with substantially no effect thereon by the impedance of the switch. By operating an electronic switch only in its high impedance and low impedance states, it is possible to minimize the effect of changes in the electronic switch due to aging, ambient conditions and the like.

It is accordingly another object of the invention to provide a constant current pulse generating circuit which comprises a constant current sink in combination with an electronic switching device which is adapted to divert the current flow from the sink into a load device for the duration of the pulse generated.

In order to produce a pulse whose output polarity is plus or minus, the present invention has utilized a transformer in combination with a pair of electronic switches which are adapted to divert the current flow in one direction or the other through the transformer so that the signal on the output windings thereof will be of a polarity dependent upon the direction of the current flow in the input winding.

It is then a still further object of the present invention to provide a circuit for generating signal pulses of one polarity or the other, where the signal pulses are of constant amplitude, by means of a pair of switching circuits co-operating with a current source where the switch circuits are adapted to selectively pass the desired current in one direction or the other through an appropriate load device.

It has been found that a very effective electronic switch exists in the semi-conductor amplifiers commonly known as transistors. These transistors generally incorporate emitter and collector electrodes which form a connection to the semi-conductor material where the impedance of the semi-conductor material may be appropriately regulated by the control or base electrode. When the transistor device is biased to its nonconducting region, it has a relatively high internal impedance. When biased to the saturated condition in the conduction region, the impedance is relatively low.

A still further more specific object of the invention is, therefore, to provide a constant current pulse generating circuit utilizing transistor devices as the active switching elements of the circuit and where these transistor devices may be operated without their internal impedance characteristics having an appreciable effect on the resultant output pulse.

The foregoing objects and features of novelty which characterize the invention as well as other objects of the invention are pointed out with particularity in the claims annexed to and forming a part of the present specification. For a better understanding of the invention, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

Of the drawings: I

FIGURE 1 illustrates a preferred embodiment of the circuit of the present invention; and

FIGURE 2 shows representative wave forms produced by the circuitry of FIGURE 1.

Referring first to FIGURE 1, the numeral 10 identifies the switching circuit used to produce the current pulse which is desired for application to a utilization circuit 11, the latter of which may take the form of a coincident current memory of the type disclosed in the aforementioned article by J. W. Forrester. The switching circuit or pulse generating circuit 10 will be seen to comprise a pair of terminals 15 and 16 which are adapted to be connected to a suitable source of power having a substantially constant voltage. output. Connected to the power source terminals and 16 is a first series circuit which comprises a resistor 17, inductor 18, a diode 19 and a current sink 20. The current sink 20 comprises a condenser 21 and a resistor 22, and a power supply 23. The latter is particularly desirable when the apparatus is used with a high duty cycle.

Connected to the junction of the inductor 18 and diode 19 is a center tap 25 of a transformer winding 26. The transformer winding 26 serves as the primary winding for a transformer 27, the latter having a secondary or output winding 28. Connected between the left end terminal ofthe primary winding 26 and the power supply terminal 15 is a switching device comprising a transistor 30. The transistor 30 includes the normal emitter, collector and base electrodes. A pair of input terminals 31 are connected to the input of a transistor 30 for purposes of switching the transistor 30 between its high impedance state and low impedance state as will be more fully explained below.

Connected between the right end of the primary winding 26 and the power supply terminal 15 is a further transistor switching device 32, the latter having the normal base, emitter and collector electrodes. Connected to the input of the transistor 32 are a pair of input terminals 33 on which a control signal is adapted to be applied for switching the transistor 32 between its high impedance state and low impedance state.

Connected to the output secondary winding 28 are a pair of output lines 35 and 36. These lines 35 and 36 are adapted to have a current pulse from the secondary winding 28 applied thereto. Connected between the lines 35 and 36 are a plurality of address selection switching devices in the form of transistors 37, 38 and 39. These transistors are used to selectively apply the current pulse on the lines 35 and 36 to one of the select lines of the memory device 11. The particular select line activated will be dependent upon which one of the control transistors 37, 38 or 39 is activated by a control signal source, not shown. The transistors 37, 38 and 39 are symmetrically conducting transistors; i.e. they are capable of passing current equally well in either direction through the emitter-collector circuit. A transistor type suitable for use in this position is Sylvania GT 847. The input circuit illustrated for the transistor 39 is representative of those for the transistors 37 and 38. Thus, a bias source is coupled to the base electrode by way of a resistor 40. A switching signal may be applied to the base electrode by way of a diode 41.

A base current will be flowing in the symmetrical transistor that is selected for switching. To minimize the effects of base current in the selected select lines, a series of diodes 42, 43 and 44 are connected to the lines and to ground. Thus, when an input pulse is applied to the base of the transistor 39, the base current will flow through the diode 44 to ground when the select current from transformer secondary 28 flows through the transistor 39 from left to right. When the select current flows in the opposite direction, the base current will flow through the line 35, the winding 28, line 36 to the select lines leading to diodes 42 and 43. This distributes the base current to the other select lines to thereby minimize the amount of base current flowing in any one line in the memory circuit and eliminate the flow in the selected select line.

In considering the operation of the present invention, it is first assumed that there are no input signals on either of the input terminals 31 and 33 and that the transistors 30 and 32 are both biased into their high impedance state. Under these conditions, a current will be flowing from the source of power and this current may be traced from the positive supply terminal 15 through the ground terminal, the sink 20, diode 19, inductor 18 and resistor 17 back to the negative terminal 16. The current flowing in this circuit will be a constant current provided a constant voltage is applied thereto at the terminals 15 and 16. Since it is desired to produce an output pulse on the winding 28,

the control signal will be applied to one or the other of the input terminals 31 or 33. When an input signal is applied to the terminals 31 to switch the transistor 30 from its high impedance state to its low impedance state, the current which was flowing through the diode 19 and the sink 20 will now be diverted therefrom and will pass through the emitter-collector circuit of the transistor 30, the left terminal of the primary 26, to the center tap 25 and thence through the inductor 18 and resistor 17 back to the negative terminal 16. The inductor 18 and the resistor 17 serve to maintain the current flow through the active section of the primary winding 26 substantially constant during the interval of the pulse produced. The output signal appearing on the lines 35 and 36 will take the form represented in FIGURE 2. The voltage signal will be as represented in FIGURE 2A. The current signal will take the form represented in FIGURE 23 and will be seen to comprise a wave having a constant amplitude throughout substantially its entire duration. The termination of the pulse is efiectcd by switching the transistor 30 back to its high impedance state so that the current will be switched back through diode 19 and into the sink 20.

Should an output pulse of opposite polarity be desired, an input signal will be applied to the input terminals 33. Thus the transistor 32 will be switched from its high impedance state to its low impedance state. When the transistor 32 is switched to its low impedance state, the current will again be diverted from sink 20 and the diode 19 to the righthand portion of the primary winding 26. This time the current will be flowing from the primary winding in a direction opposite to that resulting from the current flow switched from the transistor 30. Thus the output signal will be of opposite polarity. The output voltage appearing in the lines 35 and 36 will be as represented in FIGURE 2C while the output current on the lines 35 and 36 will be as represented in FIGURE 2D. Again the current signal will be of constant amplitude throughout substantially all of its duration. The duration of the pulse will be determined by the time that the control signal is removed from the input terminals 33 so that the transistor 32 will be switched back to its high impedance state.

Since the transistors 30 and 32, when cut off, have a very high impedance the current flow through these devices will be substantially negligible and consequently there will be substantially no power dissipated in either of these switching devices. Conversely, when the transistor devices are switched to their low impedance state, the impedance again is sufliciently low that even though a relatively large current may be flowing through the device, the resultant power dissipation in the transistor is low. While power is dissipated during the switching operation, it is likewise low. As these transistor devices are not operated in the region between the high impedance and low impedance states for any appreciable time, the resultant current flow is substantially independent of any of the characteristics of these devices in their intermediate regions where they are most subject to variation due to ambient conditions and aging. Further, the use of transistors in this configuration permits the selection of relatively inexpensive transistors when the duty cycle requirements are not excessive.

It will be readily apparent that the techniques utilized in the present pulse producing circuit may be extended to other types of circuits wherein constant current pulses are required.

While, in accordance with the provisions of the statutes, there has been illustrated and described the best forms of the invention known, it will be apparent to those skilled in the art that changes may be made in the apparatus described without departing from the spirit of the invention as set forth in the appended claims and that in some cases, certain features of the invention may be used to advantage without a corresponding use of other features.

Having now described the invention, What is claimed as new and novel and which it is desired to secure by Letters Patent is:

1. Electrical switching apparatus for selection lines of a memory circuit comprising a plurality of symmetrical switching devices adapted to be connected one each in series with each of said selection lines, said switching devices each comprising transistor elements having base electrodes to which a signal is adapted to be applied for switching the impedance thereof from a high impedance state to a low impedance state, and means for minimizing the flow of base current in said select lines comprising a plurality of diodes connected one each to said selection lines and to a terminal common to the input circuit to the base electrodes.

2. Electrical switching apparatus for selection lines of a memory circuit comprising a plurality of symmetrical switching devices to be connected one each in series with said selection lines, said switching devices each comprising transistor elements having a base electrode to which an input signal is adapted to be applied for switching the impedance thereof from a high impedance state to a low impedance state, and means for minimizing the flow of base current from a selected switching in series with a selected selection line comprising a plurality of diodes connected one each to said select lines and to a terminal 10 common to the input circuit to the base electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,907,000 Lawrence Sept. 29, 1959 2,966,597 Bonn et a1 Dec. 27, 1960 2,994,044 Straube July 25, 1961 

1. ELECTRICAL SWITCHING APPARATUS FOR SELECTION LINES OF A MEMORY CIRCUIT COMPRISING A PLURALITY OF SYMMETRICAL SWITCHING DEVICES ADAPTED TO BE CONNECTED ONE EACH IN SERIES WITH EACH OF SAID SELECTION LINES, SAID SWITCHING DEVICES EACH COMPRISING TRANSISTOR ELEMENTS HAVING BASE ELECTRODES TO WHICH A SIGNAL IS ADAPTED TO BE APPLIED FOR SWITCHING THE IMPEDANCE THEREOF FROM A HIGH IMPEDANCE 